CA1326643C - Process for the decontamination of the surface of a metal part contaminated by tritium and apparatus usable for this process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a process for decontaminating the surface of a metal part contaminated by tritium and an apparatus usable for performing this process. In order to carry out the decontamination, the part to be decontaminated is connected to the negative pole of a direct current generator, at least one portion of the surface of this part is contacted with a mixture incorporating water and an electrolyte, e.g. an aqueous solution of soda or sulphuric acid, or water and solid electrolyte, an electric current is passed between the part and an anode connected to the positive pole of the electric current generator by applying to the part to be decontaminated a current density of 10 to 50 mA.cm-2 for the cathodic hydrogen charging of the part being decontaminated and the replacement by hydrogen of the tritium adsorbed on the surface of this part.

Description

~ 3266~3 Process for the decontamination of the surface of a metal part contaminated by tritium and apparatus -~
usable for this procPss.
~ .
DESCRIPTION
The present invention relates to a process for the decontamination of the surface of metal parts contaminated with tritium. It more specifically re- -lates to an el~ctrolytic decontamination process making it possible to eliminate the tritium present on the surface of a metal part without modifying the pro- -file of the surface of said part, 50 as to optionally permit the reuse thereof. ~-This process more particularly applies to small metal parts with a compl~x geometry, to parts having a large surface area but a simple geometry, as well as to parts having relatively inaccessible areas, such as those with a contorted geometry.
Among the presently known processes for de-contaminating parts contaminate!d with radioactive ma-terials it is possible to use e!lectrolytic processes, like those described in French patents 2 490 685 and 2 533 356 and US patent 3 515 655.
In these patents, which use electrolytic pro-cesses for decontaminating metal parts, a deminerali-zation of the surface of the parts is obtained, which makes it possible to extract the radioactive particles present on said surface. These operations suf~er from the disadvantage of being destructive and of modifying the surface pro~ile of the parts, which can conse~
quently not be directly reused after treatment. More-over, the processes described in these patents do not relate to the decontamination of parts contaminated by tritium.
. . :
The present invention specifically relates to a process for the decontamination of the surface of :~ 3 ~

metal parts contaminated by tritium making it possible to obviate the disadvantages o~ the processes de-scribed hereinbefore. The process according to the invention for decontaminating the surface of a metal part contaminated by tritium comprises the following stages:
1) connecting the part to be decontaminated to the negative pole o~ a direct current generator, 2) contacting at least one portion of the surface of the part to be decontaminated with a mixture incorporating water and an electrolyte able to rel~ase hydrogen by electrolysis, and 3) passing an electric current between the part to be decontaminated and an anode connected to the posi-tive pole of the electric current generator and in contact with the mixture incorporating water and an electrolyte, by applying to the part to be de-contaminated a current density of 10 to 50 mA/cm2 and preferably 10 to 25 mA/cm2 in order to cathod-ically charge with hydrogen the surface of ~he part to be decontaminated and thus replace by the hydrogen the tritium adsorbed on the surface of the part to be decontaminated.
ThP process according to the invention uses low current densities, which make it possible to effect a cathodic hydrogen charging of the surface of the partO Thus, through the choice o~ current densi-ties of 10 to 50 and preferably 10 to 25 mA~cm2, the -~
hydrogen can be adsorbed on the surface o~ the part, whereas in the prior art processes, such as that o~ US
patent 3 515 655, higher current densities are used -~
and there i8 a significant evolution of hydrogen, --which assists decohesion o~ the metal. This leads to the growth of cavities and cracks and consequently 3S surface par~icles are torn away and the treated part ~-undergoes demetallization. -': ' ' ~ :, :~32~3 ::

;; Thus, at current densities of lO to 25 mA/cm2, the hydrogen formed by electrolysis is largely . adsorbed on the surface of the cathode. At current . densities of 2~ to 50 mA/cm2, there is simultaneously ; 5 an adsorption of the hydrogen on the cathode and an evolution of gaseous hydrogen, whilst at current densities above 50 mA/cm2, there is only an avolution ~, o~ gaseous hydroyen.
Thus, in the case of the process of US patent 3 515 655, there is no cathodic hydrogPn charging, but solely a gaseous hydrogen evolution, which leads to ~, the tearing away of the metal particles and the radio-active particles deposited on the sur~ace to be de-~ comtaminated. Moreovex, it is not a question of ~ 15 tritium and, with radioactive particles other than tritium, there would be no decontamination at current densities below 50 mA/cm2 and there would only be a j hydrogen charging of the part.
In the inYention ~ the hydrogen is released in .1 20 the same way as in the prior art processes by the ,l ~ollowing reaction: 2H20 + 2e ~ 2H + 20H, but the released hydrogen quantity is ]Lower and it then reacts :~
with the tritium adsorbed on the surface of the part in accordance with two mechanisms, which are illus-trated by the ~ollowing reactions:
a) adsorption o~ hydrogen and insertion of tritium ~ :
into deeper layers of the part: :~
H ~ MTads + M ~ ~i Hads + MTins in which M represents the metal or metals con-stituting the part, ads means adsorbed and ins means inserted and ..
b) trans~er of tritium into th~ water-electrolyte mixture: :
H + NTads ~ MHads + T .:
in whlch M and ads have the meanings given herein- : :
be~ore.
-. ...

;" .;,i , `i .. '. ~' ';: ;!, . ' - 4 ~ ~ ~2~ ~ 3 These reaction mechanisms are governed by different parameters, such as electrochemical para-meters, e.g. the curren~ density, cathodic overvoltage and the nature of the electrolyte, the temperature and the electrolysis time.
Thus, when the cathodic overvoltage is at a correct value hydrogen adsorption is assisted and the energy vaxiation between H-M and T~M leads to the insertion of tritium into the part and the transfPr of tritium into the water.
At the end o~ the operation, a part is obtained, whose sur~ace is charged with hydrogen, a water~electrolyte mixture containing part of the ~-tritium present on the sur~ace of the part and tritium - -inserted into khe deeper layers of the part.
The replacement of the tritium adsorbed on the surface o~ the part by hydrogan makes it possible I to form a hydrogen barrier, which blocks the ba~k diffusion of tritium inserted into the part. There-fore this proce~s is of yreat interest, because the surface layers of the part are not damaged and the part can be recy~led after trsatment.
Generally the mixture incorporating water and an electrolyte is constituted by an aqueous solution of an electrolyte chosen in ~uch a way ~hat the aque- ~-ous solution can release hydrogen by electrolysis.
For example, this electrolyte can be sulphuric acid or an alkali metal hydroxide such as soda. Preference is given to the use o~ soda, because it delays the evo-3Q lution of hydrogen. In the case of sulphuric acid, there is an etching of the metal as from 50 mA/cm2 and the etching speed, i.e~ the corrosion 9 increases as from said value with the current density.
Pre~erably, the electrolyte concentration o~ -the ~olution i5 low, in order to avoid corrosion of the part to be treated. It is there~ore conventional _ 5 _ ~3~ 3 ~.
practics to use aqueous solutions containing Ool to 1 mole.L 1 of sulphuric acid or alkali metal hydroxide, such as NaOH.
However, it is also possible to use more concentrated olutions, but this is not really of ~
interest, because the ef~luents obtain,od are much more ~ ~-di~icult to treat.
3 According to a first embodiment of the pro-cess according to the invention, which is particularly appropriate for the treatment of small parts, the part to be decontaminated is immersed in water or an aque~
ous solution, preferably constituted by an aqueous ¦ electrolyte solution, such as those described herein-before. In this case, the anode can be also immersed in water or the aqueous solution. However, it is more advantageous to use as the anode the vessel containing ¦ the water or a clear solution. This vessel can e.g.
be made from graphite impregnat:ed with polytetra-' fluoroethylene wax, which i5 resistant to chemical ¦ 20 etching and has no porosity as compared with pure graphite. As a result the water or aqueous solution cannot pass through the vessel by capillarity.
In this embodiment of the inventive process, ~! it is possible to simultaneously treat several parts ~i ~ 25 by placing them in an electricity conducting basket connected to the nsgative pole of a dir,Pct current generator.
According to a second embodiment of the pro-cess, more particularly suitable for the treatment of large parts, electrolysis is e~fected by using the so-called buffer electrolysis method. In this case an ~ assembly comprising the anode and a solid electrolyt 3~ iS passed over the surface of the part and water is circulated between the sol,id electrolyte, the anode -~
and the surface of the part to be decontaminated.
.
~ ~ The solid electrolyte can be constituted by , .::

. .

- 6 - ~ 3~

an ionic conductive polymer, which is ionizable by water or an aqueous solutionO It is e.y. possible to use perfluorosulphonic acid of formula:

-~CF2 - CF2 - ~F - CF - CF2~-n in which R represents an organic radical and n is a :~
polymerization number, which is ionizable by pure water. -:~
. :.
This embodiment of the process is advantage- -.
ous becau~e it makes it possible to eliminate the use of ch~mical agents in ~olution, which are responsible for corrosion, as well as the problems of the re- :~-processing of effluents. Moreover, it makes it possi-ble to decontaminate more highly tritiated zones and to reach zones which are not very accessible by oth~r :-2U treatments. Finally, it is adapted to the realisation :~
of an in situ decontamination and also leads to little ~ritiated waste.
In this ~acond embodiment of the process, the .~--anode can be made from ~raphit~ impregnated or not i 25 with polytetrafluoroethylene wax.
In general, for carrying out the decontami-natlon according to this second embodiment, use is .:;~
made of an assembly having an anod~ and a solid elec-trol~te and which is provided with means for bringing l 30 about circulation of the water or aqueous solution ~ :`
~ between the anode/ the solid electrolyte and the part `. : to be decontaminated. ~-i~ .
~: The present invention also relates to an : apparatus for the electrolytic treatment of the sur- :-35 face of a metal part~ characterized in that it com-prises a hollow electricity conducting material body ::

: '' ,:;

~ 7 ~ ~ ~ ~fi~3 connected to one of the poles of an electric current generator, the hollow body being provided with at least one liquid outlet port to which is applied a porous, permeable element made from electricity con-ducting material, a solid electrolyte applied to theouter surface of the porous, permeable element and mean~ for displacing the hollow body on the surface of the part to bP treated, so that the solid electrolyte is in contact with the part and means for introducing a liquid into the hollow body and ~or circula~ing it through the outlet port between the porous, permeable electricity conducting material element and the sur-face of the part to be treated.
The hollow body, which in the inventive pro-cess constitutes the anode of the apparatus, can be made from polytetrafluoroethylene wax-impregnated gra- ::
phite and the porous, permeable element can be con-stituted by a graphite felt. The solid electrolyte applied to the outer surface of the porous element can be made from an ionic conductivl~ polymer, ionizable by water or an aqueous solution, P.g. of perfluoro carb-oxylic sulphonic acid.
According to a variant of these embodiments, more particularly suitable for the treatment of small ` -parts with a contorted geometry, it is possible to move an assembly comprising the anode and the solid electrolyte over the surface of the parts to be de-contaminated and which are immersed in water. In this case, the solid electrolyte-anode assembly can be con-stituted by a graphite part having on one o~ its faces a grahite felt externally coated with the solid elec- .
trolyte, e.g. an ionic conductive solid polymer.
According to a variant of the second embodi-ment, it is also possible to use an anode-solid ele trolyte-cathode sandwich. In this case, the appa-ratus also comprises a cathodic element of palladium . .
. ''~ ' ",~

- 8 - ~32~3 black and/or nickel into which the hydrogen can dif-fuse, said element being applied to the solid elec- ~ ;
trolyte, in such a way that when the hydrogen has -diffused into said element, it is directly implanted in the par~ to be decontaminated. In this variant, the cathodic face of the solid electrolyte can be successively coated with palladium black by impreg-nation and nickel over a thickness of 250 microns.
The palladium black can be deposited from palladium salts n aqueous solution and then the nickel can be deposited by metallization by the chemical route or cathodic sputtering, followed by the electrolysis of a nickel salt.
In this variant, the hydrogen diffuses into ~5 the nickel cathode. The atomic hydrogen is recovered on the opposite face and i5 directly implanted on the part to be decontaminated, whic:h is attached to said assembly.
In this variant, it ic; also possible to use an anode-solid electrolyte-cathode sandwich, in which the Pd ~nd/or Ni black forming the cathodic adsorption ~ ielement are fitted into the unclerlying layers of the ;~ solid electrolyte. This has the advantage of increas- ~;
ing the adsorption surface of the cathodic hydrogen on the part to be decontaminated.
For example, it is possible to obtain this sandwich structure by impregnating the conductive polymer with an ionic compound of Ni or palladium, which is not an anionic ~omplex, e.g. NiCL2 or Pd(N03)2 and by soaking the polymer in a 25~ dimethyl aminoborane ~olution at 85C. Under these conditions, this organic compound decomposes and gives rise to atomic hydrogen within the polymer and said hydrogen chem~cally reduces the Pd2+ or Ni2~ cations to the finely divided metal state in the ~irst underlying ; layers of the polymer.

. .

- 9 - 1 3 ~ 3 The parts which can be decontaminated by the inventive process can be made from different metals and alloys, provided that the electrolyte and the electrolysis conditions are chosen in such a way as to prevent corrosion of the material. For example, the process can apply to the treatment of stainless steel parts or parts made ~rom copper alloys, e.g. o~ brass.
The process according to the invention can be performed at ambient temperature, but ik is also possible to operate at higher temperatures, but be-cause the temperature plays a significant part with :
respect to the insertion of the tritium into the deep layers of the part. Thus, the quantity of adsorbed H
or T decreases with the temperature during el~ctrol- -~
ysis. In the same way, the dif~usion of H or T into the cathode increases with the temperature. There is a slight back diffusion, but mo~t of the H or T --remains blocked in the metal and blocking becomes even greater on return to ambient te]mpexature.
It is also preferable to operate at tempera-tures above the ambient temperature, whilst avoiding corrosion risks, e.g. at temperatures of 25 ta 100C
and especially 80C.
In the process according to the invention, : 25 the electrolysis duration also constitut2s an im- -~
portant parameter, because it acts on the eliminated tritium quantityO However, in the first embodiment of ~ --the process, where the parts are immersed in water or an aqueous solution, at the end of a certain time a balance is obtained between the tritium concentration in the water or aqueous sollltion and the tritium concentration in the part to be treated. Thus, this -: :~
~: corresponds to the following reaction: .:

T + H23~iHTO ~ H : ~
"'~ ' '"

'" .;i' ' ':

- lo ~ 3 Furthermore, if in the ~irst embodiment of the proces~ it is wished to obtain a higher decontami- ~ -nation ratio, it is necessary to carry out successive-ly several decontamination cyclas on the same part .:
using for each cycle a new aqueous solution or a new wat~r chaxge, Other features and advantages of the inven~
tion can be gathered from the following des~ription relative to an embodlment and ~he ~ttached drawings, ~0 wherein show:
Fig. 1 a graph showing the evolution of the dPcontamination ratio as a ~unction of the treatment time.
Fig. 2 a graph showing the evolution of the tritium surface activity of a part as a function of khe numb~r of decontamination cycles.
Fig. 3 diagrammakically an anode-mobile electrolyte assembly usable in the second embodiment o~ the inventive process.
Fig. 4 diagrammatically the anode-solid -~
electrolyte polymer-mobile nickel and palladium black cathode assembly usable in the case of the implan-tation of atomic diffusion hydrogen.
The following examples relate to the de- :
contamination of parts made ~xom stainless steel or brass contaminated by tritium. : :

This example involves the surface decontami- :
nation of stainless steel parts using the fir~t em-bodiment sf the process, i.e. immersion of the parts in an aqueous solution containing 1 mole.L 1 of NaOH, placed in a heated polytetrafluoroethylene wax-impregnated graphite vessel, which constitutes the anode of the apparatus. Working takes place with a -~
current density applied t9 the surfac~ of the parts of 10 mAOcm ~, at a temperature of 80C and electrolysis :.:
'.'.'' ,'' is perfo~med for two hours.
At the end o~ this treatment, the tritium de-contamination ratio (DR) is determined and this corre-sponds to the tritium surface activity ratio of the part before treatment to the surface activity of the part after treatment. The thickness loss of the part is also determined.
This is ~ollowed by 12 identisal treatment cycles using for each cycle a new aqueous NaOH so-lution and the tritium decontamination ratio is de~termined after these 12 cycles. The results obtained are yiven in Table 1, where the electrolytic treatment conditions are also indicated.
EX~PLE 2 ~n this example brass parts are treated in the same way as in Example 1, but using an a~ueous solution containing 1 mole.L 1 of sulphuric acid in place of the agueous NaOH solution. As hereinbefore, the decontamination ratio and the thickness loss of the par~ are determined after a treatment cycle. The results obtained are also given in Table 1.

This example studies the influence of the ~lectrolysis time on the decontamination ratio ob~
tained. Electrolysis is per~ormed under the con-ditions of Example 1 on stainless steel parts and the surface activity of the part i~ measured as a function of the duration of electrolysis performed in the same solution.
The results obtained are given in Fig. 1, w~ich repr~sents the increase in the surfacs de~
contamination ratio (DR) as a function of the elec~
trolysis time in hours. It can be seen that the decontamination ratio virtually no longer increases a~ter two hoursl due to the equilibrium established between the tritium concentration of the solution and "~ ' .
: :. .

- 12 - ~3~ 3 the tritium concentration of th~ part, as has been shown hereinbefore.

In this example different stainless steel parts are decontaminated by using the electrolysis conditions of Example 1 and treatment cycles lasting two hours.
Several treatment cycles are successively performed on ~ive parts constituted by a ball (part 1), a ~lask (part 2), a collar ~part 3), a rod (part ~:~
4) and another Xlask (part 5~ and after each cycle the tritium surface actiYity of the parts is determined (in micro Ci.cm~2).
The results obtained are given in Fig. 2, which repre~ents the evolution of the surface activity of the parts as a function o~ the number o~ treatment cycles. urves 1,~,3,4 and 5 r~espectively relate to part~ 1,2,3,4 and 5. It can be s~en that in all cases the sur~ace activity of the part decreases with the number of treatment cycles~ -EXAMPLE S
.. . .
This ~xample illustrates the use of the so- :
called buffer process ~or decontaminating stainless steel parts. This example uses the apparatus dia- :~
~rammatically shown in Fig. 3, which comprises an ~.
anode constituted by a hollow polytetra~luoroethylene :::
wax-impregnated graphite cylinder 1, which is provided at its base with an outlet port la, tc which is applied a porous, permeable graphit2 felt element 2 :
and a solid ionic conductive polymer film 3, constitu~
ted by per~luoro sulphonic acid, the felt and the film 3 being ~ixed to cylinder 1 by appropriate means not shown in t~e drawing.
The hollow graphite cylinder 1 is also pro vided with a li~uid introduction ori~ice lb by which ~- water can be circulated in the hollow anodic cylinder, ~ .
~' ,'~', ~ .

- 13 - ~ 3 2 ~ ~ ~ 3 the water then flowing through orifice la through the graphite felt 2 and the ionic conductive polymer film 3. The hollow graphite cylinder can be conn~cted to the positive pol4 o~ the electric current generator 5 and it can be displaced in the three directions in space by any appropriate means, e.g~ by an automatic laboratory d~vice 7.
This device can be used for decontaminating the flat part 9, which is connected to the negative ; 10 pol~ of generator 50 Under these conditions, the hollow graphite cylinder 1 i~ moved ~o bring it into contact with the part, so as to circulate water in the graphite cylinder 1 through the gra~hite felt 2 and the ionic conductive polymer film 3 on the surface o~
the part. The assembly is moved on part 9 and the ::
speed and displacement mode is regulated so as to ~ -obtain a satisfactory decontamination. : -For example, a ~evice of this type was used for decontaminating a stainless ste~l plate using a current density on the plate of 10 to 50 mA.cm 2 and a hollow cylinder displacement speed of 40 cm.min 1.
~he to~al time for carrying out: the decontamination of ~-a 10 cm2 plate with a length of 10 cm is one hour.
The tri~ium decontamination ratio of the :~
surface o~ the part and the thickness loss are then determined as hereinbefore. ~he results obtained and treatment conditions are given in Table 2.
Thu~, a gcod decontamination rakio can be :::
obtained with a negligible thickness loss.
In this type of device the operating tempera-ture is abo~e ambient tempsrature, due to the Joule ; effect obtained by electrolysis.
EX~MPLE 6 This is a variant of Example 5, where use is - ;
made of the property of t~e diffusability of atomic hydrogen into a nickel cathode. Use is made of the '~ ' .
;~ j . .

- . .

~ 3 ~
apparatus diagrammatically shown in Fig. 4, which is identical to that of Fig. 3, but to which has been add~d a 250 ~m palladium black and nickel cathode 4 between the ionic conductive polymer film and the plate to be decontaminated. This ~pparatus has ori-fice lc for the discharge of the water contained in the hollow cylinder 1. :
For example, use was made o~ an apparatus of this type for decontaminating a stainliPss steel plat~
by using a current density on the plate of 20 mA.cm 2, an electrolyte temperature between 50 and 80C and a hollow cylinder displacement speed of 40 to 200 cm~min 1. The total number of cycles for performing the decontamination of a 10 cm2 plate with a length of :-lO cm is 700.
The tritium decontamination ratio of the sur-~ace of the part is determin~d in the same way. In this case, it undergoes no thickness loss and it is `
possible to use materials which are degraded by cath- .:
odic polarization and electrolytes, such as alloys o~
aluminium and copper. The results obtained and the processing conditions are given in the following Table 3.
~XAMPLE '7 -:.
In this example, use is made of the first embodiment of the inventive process for treating a stainlass steel part with average dimensions and a complicated geometry constituted by a valve, whose orifice is highly contaminated by tritium. The part is placed in a tank containing water and into the orifice to be decontaminated is introduced an anode-solid electrolyte assembly constituted by a graphite rod covered with graphite ~elt and an ionic conductive solid polymer film.
Electrolysis is performed with a current density of lO mA.cm 2 for two hours at the temperature ~32~3 obtained by the Joule effect due to electrolysis. At the end o~ the operation, the tritium decontamination ratio of the surface of the part and its thickness loss in micrometres ar~ determined. The results ob-tained and khe treatment conditions are given in Table 4. :
The invention is not limited to the embodi-ments envisaged or described hereinbefore. In partic-ular, ~or the so-called buf~er electrolysis process, ~0 it is possible to use conventional equipment, like those described in French pAtents 2 490 685 and 2 533 356~ It is also possible to use other materials ~or producing the anodes used in the inventivs pro-cess, as well as other materials as solid electro-lytes, which can be associated with water or appro-priat~ aqueous solutions. Moreover, when using the buf~er electrolysis process, it is possible to employ electrolytes in aqueous solution, e.g. a soda solution -:
or a sulphuric acid solution.
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TABLE 4 ~
~.-Example 7 Ele~tro- Time Current Thickness DR
(treated lyte (hours3 density loss (,um3 material) (mA.cm 23 , 2 ~:
stainless H20 + 2 10 10 10 steel perfluorO
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Claims (19)

1. Process for the decontamination of the surface of a metal part contaminated by tritium, characterized in that it comprises the following stages:
1) connecting the part to be decontaminated to a negative pole of an electric direct current generator;

2) contacting at least one portion of the surface of the part to be decontaminated with a mixture incorporating water and an electrolyte able to release hydrogen by electrolysis; and

3) passing an electric current between the part to be decontaminated and an anode connected to a positive pole of said electric direct current generator and in contact: with said mixture incorporating water and an electrolyte, by applying to the part to be decontaminated a current density of 10 to 50 mA/cm2 in order to cathodically charge with hydrogen the surface of the part to be decontaminated and thus replace by the hydrogen the tritium adsorbed on the surface of said part to be decontaminated.

2. Process according to claim 1, wherein said current density applied to the part to be decontaminated is of 10 to 25 mA/cm2.

3. Process according to claim 1 or 2, characterized in that said mixture incorporating water and an electrolyte is constituted by an aqueous solution of alkali metal hydroxide or sulphuric acid.

4. Process according to claim 1 or 2, characterized in that said mixture incorporating water and an electrolyte is constituted by an aqueous soda solution.

5. Process according to claim 1 or 2, characterized in that the anode is made from polytetrafluoroethylene wax-impregnated graphite.

6. Process according to claim 1 or 2, characterized in that the part to be decontaminated is immersed in water or aqueous solution.

7. Process according to claim 6, characterized in that the anode is constituted by a vessel containing the water-electrolyte mixture.

8. Process according to claim 1 or 2, characterized in that the electrolyte is a solid electrolyte.

9. Process according to claim 8, characterized in that the solid electrolyte is an ionic conductive polymer.

10. Process according to claim 9, characterized in that the solid electrolyte is perfluoro sulphonic acid of formula:

in which R represents an organic radical and n is a polymerization number.

11. Process a cording to claim 8, characterized in that an assembly incorporating the anode and the solid electrolyte is moved over the surface of the part to be decontaminated and in that water or an aqueous solution is circulated between the anode, the solid electrolyte and the surface of the part to be decontaminated.

12. Process according to claim 1 or 2, characterized in that the part to be decontaminated is of stainless steel or a copper alloy.

13. Apparatus for the decontamination of the surface of a metal part contaminated by tritium, characterized in that it comprises a hollow electricity conducting material body connected to one pole of an electric current generator, the hollow body being provided with at least one liquid outlet port to which is applied a porous, permeable element made of electricity conducting material, a solid electrolyte applied to an outer surface of the porous, permeable element and means for displacing the hollow body on the surface of the part to be decontaminated, so that the solid electrolyte is in contact with said part, and means for introducing a liquid into the hollow body and for circulating it through the at least one outlet port between the porous, permeable element made of electricity conducting material and the surface of the park to be decontaminated.

14. Apparatus according to claim 13, characterized in that said body is of polytetrafluoroethylene wax-impregnated graphite.

15. Apparatus according to claim 13, characterized in that the porous, permeable element is of graphite felt.

16. Apparatus according to claim 13, characterized in that the solid electrolyte is an ionic conductive polymer.

17. Apparatus according to claim 13, characterized in that it also comprises a cathodic palladium black and/or nickel element in which hydrogen can diffuse, said cathodic element being applied to the solid electrolyte in such a way that when the hydrogen has diffused into said cathodic element, it is directly implanted in the part to be decontaminated.

18. Apparatus according to claim 17, characterized in that said cathodic element is fitted into the solid electrolyte.

19. Apparatus according to claim 17, characterized in that the cathodic element has a thickness of approximately 250µm.